Two senators are pressing federal authorities to crack down on an online black market and “untraceable” digital currency known as Bitcoins after reports that they are used to buy illegal drugs anonymously.

Democratic Senators Charles Schumer of New York and Joe Manchin of West Virginia wrote to Attorney General Eric Holder and Drug Enforcement Administration head Michele Leonhart in a letter that expressed concerns about the underground website “Silk Road” and the use of Bitcoins to make purchases there.

The letter prompted a discussion among Bitcoin enthusiasts about whether the government was capable of closing related bank accounts and thereby stifling the currency.

The senators released a copy of their letter on Monday. It cites recent media reports that some tech-savvy individuals were using an “anonymizing network” known as Tor to gain clandestine access to Silk Road and buy illegal drugs.